A major shortcoming of Receiver Autonomous Integrity Monitoring (RAIM) Fault Detection and Exclusion (FDE) is widely recognized to be its occasional lack of availability, in the sense that the integrity level it can protect in any given situation cannot always be smaller than the required alert limit for a given flight operation. Ever since the RAIM FDE algorithms were developed, accepted and published more than ten years ago, the system availability has been bound, by and large, to the limitations of its monitoring mechanism to be able to detect and exclude a single measurement fault. There have been many studies made on evaluating the system availability, usually on a global basis, and they have considered various assumptions of constellation size, horizon mask angle, and aiding with baro-altitude, inertial, and additional non-GPS satellites, or even with Loran. In all of these studies, however, the basic shortcomings of RAIM FDE remained essentially bound by its theoretical limits. There has been a recent proposition that departs from conventional assumptions made in the standard RAIM-FDE by better balancing accuracy and integrity levels. This proposition results in the lowering of the horizontal integrity limit for all satellite measurement geometries, thereby improving system availability in the process.
More recently as disclosed in the incorporated patent applications a methodology called Novel Integrity Optimized RAIM (NIORAIM) had been used to reduce the protection or integrity limit for a given GPS satellite geometry. This method takes in, as its inputs, all the raw pseudorange measurements of a GPS receiver, determines the proper set of weights on each measurement to intentionally form a suboptimal position solution that would then has the best (lowest) protection limit possible for integrity purposes. The algorithm was designed for integrity assurance of the horizontal position with the idea that it can also be further generalized to other parameters. The NIORAIM computational algorithm is more complex than the standard form of RAIM and requires a four-dimensional lookup table to reduce its real-time processing burden.
There has been more recent interest placed on assuring integrity for vertical positioning applications for aircraft approach into airports, and there is potential to use Galileo satellites to augment the GPS constellation to produce acceptable vertical protection limits for such operations. An anticipated requirement by the FAA is to segment GPS and Galileo solutions. An advantage this segmentation has is the allowance for multiple faults to occur within one system.
Accordingly, there is a need for NIORAIM principles to be applied to the case of multiple segmented position solutions. There is also a need to simplify computations in such a process.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.